The present invention relates to monitoring during chemical mechanical polishing.
An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive or insulating layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface, and gradually removing the filler layer along a plane, i.e., planarizing the filler layer, until the non-planar surface is exposed. For example, a conductive filler layer can be deposited on a patterned insulating layer to fill the trenches or holes in the insulating layer. The filler layer is then polished until the raised pattern of the insulating layer is exposed. The portions of the conductive layer remaining between the raised pattern of the insulating layer form vias, plugs and lines that provide conductive paths between thin film circuits on the substrate. Alternatively, an outmost dielectric or semiconductor layer of a substrate can be planarized.
Chemical mechanical polishing (CMP) is one accepted method of planarization. At a polishing station, the substrate is typically mounted on a carrier head (also called polishing head) and faces a polishing pad (also called polishing disk pad or belt pad) mounted on a rotating platen. The carrier head also rotates and pushes the substrate against the polishing pad with a controllable load. The rotation rate of the platen is typically very close to the rotation rate of the carrier head to avoid uneven polishing due to a non-vanishing average of linear velocities at each point of the substrate. A polishing slurry, including at least one chemically reactive agent, can be supplied on the surface of the polishing pad.
Polishing the substrate can be monitored in situ, i.e., during polishing, or by removing the substrate from the polishing station and transferring it to a metrology station. In-situ monitoring has been implemented using, e.g., optical and/or eddy current sensors mounted in the platen. Other techniques propose monitoring friction, motor current, slurry chemistry, acoustics, or conductivity. The substrate is typically monitored for endpoint detection, i.e., detecting whether the polishing process is complete, e.g., whether a substrate layer has been planarized to a desired flatness or thickness, or when a desired amount of material has been removed.